Datasheet
LMV1089
NEAR
SPEECH
OPTIMIZED
SPEECH
WRONG
TIME (200 ms/DIV)
IDD (5 mA/DIV)
CAL start
Program start
CAL ready
LMV1089
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
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SUPPLY CURRENT DURING CALIBRATION
The calibration function performs two main tasks in a sequence. First the AC characteristics of the microphones
are matched. Then in the second stage, if the PE pin is high, the on-chip EEPROM is programmed.
During the first stage of this sequence the supply current on the LMV1089 will increase to about 2.5mA. During
the writing of the EEPROM the supply current will rise for about 215 ms to about 30mA. This increased current is
used for the on chip charge pump which generates the high voltages that are required for programming the
EEPROM.
Microphone Placement
Because the LMV1089 is a microphone array Far Field Noise Reduction solution, proper microphone placement
is critical for optimum performance. Two things need to be considered: The spacing between the two
microphones and the position of the two microphones relative to near field source
If the spacing between the two microphones is too small, near field speech will be canceled along with the far
field noise. Conversely, if the spacing between the two microphones is large, the far field noise reduction
performance will be degraded. The optimum spacing between Mic 1 and Mic 2 is 1.5-2.5cm. This range provides
a balance of minimal near field speech loss and maximum far field noise reduction.
The microphones should be in line with the desired sound source 'near speech' and configured in an endfire
array (see Figure 34) orientation from the sound source. If the 'near speech' (desired sound source) is
equidistant to the source like a broadside array (see Figure 33) the result will be a great deal of near field speech
loss.
Figure 33. Broadside Array (WRONG)
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